The present invention relates to a device for clamping and unclamping dental tools, e.g., drills, in a dental handpiece with an angled head in which the tool is held by means of a two-part clamping device. One part of this clamping device is in the form of a collet which holds the tool, and the other part is in the form of a driven rotary hollow shaft located in the head. Inside the hollow shaft, the collet can be moved lengthwise. In order to assume its clamped or unclamped position, collet and collet shaft can be threaded into one another by means of an outside thread on the collet and an inside thread in the hollow shaft. One of the two parts of the two-part clamping device is provided at the tool end of the head with at least one key surface accessible from the outside. The other part of the two-part clamping device on the end opposite to the tool end of the head also has at least one key surface accessible from the outside.
The device for clamping and unclamping comprises an essentially U-shaped carrier whose one flange has a stationary key with engaging means for engagement with the key surfaces located at the tool end of the head. The other flange has a pin-like key which projects into the area between the two flanges and is axially movable in an axial hollow space of an outside attachment of the flange against the action of a spring in the direction away from the first flange. This pin-like key can be rotated manually by means of a knob on the key end projecting from the attachment and, at the end opposite the knob, has engaging means for engaging the key surfaces located at the end opposite the tool end of the head.
In such devices, due to the movement of the pin-like key against the action of the spring, i.e., in the direction away from the opposite flange, the end of this key which is provided with engaging means is moved in the direction of the outside attachment of the flange receiving the pin-like key so that there is enough room for introducing the head of the dental handpiece into the region between the two flanges. At the same time, the user aligns and engages the key surfaces provided at both ends of the dental handpiece with the engaging means of both the stationary and the pin-like key. The pin-like key, under the action of the spring, is moved back to the aforementioned engagement position.
By holding the handpiece with one hand and turning the head of the pin-like key with the other hand, with the head or the part of the dental handpiece adjoining the head contacting the stringer of the U-shaped carrier, that part of the two-piece clamping device of the head of the dental handpiece whose key surfaces engage the engaging means of the pin-like key, can now be twisted so that the aforementioned part is threaded into the other part of the clamping device. The collet performs a lengthwise motion in relation to the hollow shaft so that the collet, depending on the rotation of the head of the pin-like key, opens to release a clamped tool or closes for clamping a loosely inserted tool.
A device of this type is known from the brochure "STARFLITE futura" issued by Star Dental Mfg. Co., Inc. With this known device, the knob of this key, which is heavier then the remaining pin-like key, is both the actuating member for turning the key and the actuating member for the motion of the key against the action of the spring. The latter motion must be accomplished by pulling the knob against the action of the spring, which is cumbersome and difficult, since only one hand is available while the other hand holds the handpiece. In addition, the same hand must also turn the knob in the pulled state which still under the tension of the spring, thereby increasing the complexity of handling.
Only a relatively weak spring can be used, since otherwise the finger force of the hand holding the U-shaped carrier of the device would be too small for pulling the knob and the pin-like key in the axial direction against the action of the spring. However, a weak spring impairs the exact centering of the engaging means of the two keys with the key surfaces of the head in the dental handpiece.
It is, therefore, an object of the present invention to provide a device of the initially described type which makes possible convenient operation with only one hand at substantially small costs.
Another object of the present invention is to provide a device of the foregoing character, which is substantially reliable in operation and has a long operating life.
A further object of the present invention is to provide a dental device, as described, which may be economically maintained in service.